It's not laziness, it's basic cost/benefit evaluation. Many feel that 2.7 isn't lacking in such a way that 3.x offers so great a benefit as to outweigh its cost

It's not laziness, it's basic cost/benefit evaluation. Many feel that 2.7 isn't lacking in such a way that 3.x offers so great a benefit as to outweigh its costs (effort to convert, loss of some portion of the long tail of available packages.) Others disagree. The success of 2.7 is an amazing thing. Most languages have one great major version, some have zero, Python has two.